活塞冷却油腔位置变化对活塞温度场的影响

为提升活塞油腔对活塞的冷却效果,采用ANSYS有限元分析法对活塞温度场进行数值模拟,对活塞顶部燃烧室喉口及活塞第一环槽处两个重点区域进行分析,并对活塞产生热应力具有明显影响的温度梯度进行同步分析,结果表明,内冷油腔沿活塞轴向移动时的活塞温度场变化明显大于其沿活塞径向移动时的温度场变化,对活塞高温区域的冷却效果更好。     

活塞顶面热障涂层对活塞热负荷的影响

活塞顶面热障涂层可以有效降低活塞工作热负荷、提高活塞使用寿命。以一款非道路高压共轨柴油机铝合金活塞为研究对象,采用硬度塞测温法试验测试了无热障涂层活塞在最大转矩工况下表面19个特征点的温度值,同时采用等参法建立了活塞有限元仿真分析模型,对比分析了活塞顶面热障涂层对活塞温度场和热应力场的影响。研究结果表明：活塞顶面热障涂层能有效降低活塞头部和环槽区域的工作温度,活塞头部顶面区域温度下降幅度为20~32 ℃,一环和二环的环槽区域温度下降幅度为15~18 ℃;但活塞顶面采用热障涂层后,活塞基体顶面黏结层区域的热应力会急剧升高,活塞基体顶面、喉口区域以及边缘棱角处热应力集中现象明显,在活塞顶面喉口黏结层区域最大热应力达到291MPa,易导致热障涂层的剥落失效。     

振荡油腔位置对柴油机活塞温度场的影响

针对策柴油机活塞在工况下第一环槽温度过高,导致润滑油结肢的问题,提出了降低热负荷的改进方案,探讨了由活塞振荡冷却油腔上移对活塞温度场带来影响,通过对比振荡冷却油腔上移1～4mm活塞温度场、应力场的变化,分析了采用改变振荡油腔位置来降低活塞第一环槽热负荷方法的可行性,提出了在使用提升振荡冷却油腔的方法来降低活塞热负荷时,对油腔提升高度的控制范围.     

水滴形活塞冷却油腔振荡传热数值模拟与优化

利用FLUENT软件中的VOF多相流模型对某发动机水滴形活塞内冷却油腔中机油的振荡传热过程进行了数值模拟,分析了机油在活塞内振荡流动时空气和机油的体积分数瞬态分布情况,得到了壁面传热系数随活塞转速、行程和机油填充率的变化规律。分析结果表明,活塞壁面传热系数随着行程和转速的上升而上升,转速对传热系数的影响最为显著。但随着充油率的上升,传热系数先上升后下降,最佳充油率范围在30%-50%之间。采用正交试验设计方法获得了最优方案,并与该发动机原方案进行了对比,结果表明优化方案的壁面传热系数比原设计方案提高了约16%。     

冷却油腔形状对发动机活塞振荡传热效果的影响

随着柴油机功率的不断提升,柴油机的热损伤事故时有发生,活塞冷却成为了一个必须面对的研究课题。针对不同形式的活塞冷却油腔结构对传热效果的影响开展研究,采用数值模拟的方法对圆形、椭圆形和水滴形三种冷却油腔截面形状在不同转角、柴油机转速和曲轴行程条件下进行壁面平均传热系数分析,结果标明水滴形油腔的冷却效果最优,因此在柴油机活塞结构设计时,应选用水滴形冷却截面油腔结构。     

工程车辆发动机润滑系统的常见故障诊排

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

上海帕萨特轿车发动机的故障诊修8例

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

柴油机活塞阳极氧化对结构可靠性的影响

为了探究氧化层对活塞结构可靠性的影响,以柴油机铝质活塞为研究对象建立活塞三维模型,结合试验数据对活塞温度场、热应力场和热机耦合场进行有限元模拟计算和对比分析。分析结果表明,在最大负荷工况下,阳极氧化的铝基体活塞最高温度和最大热应力较原始活塞分别下降6.58℃和14.1MPa;阳极氧化区域产生了拉应力。因此,在设计中,原始活塞顶面受压应力的区域应覆盖氧化层以平衡压应力,在原始活塞顶面受拉应力的区域应不覆盖氧化层以避免增大拉应力。活塞顶面应力状态得到改善后可以减少顶面裂纹产生,提高活塞的使用寿命。     

气门冲击淬火调高阳压温度不升原因分析

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

铝硅合金电子束焊

现代大马力发动机多采用双金属内冷油腔铝硅合金活塞。这种活塞由铸造活塞顶与锻造活塞裙焊接而成。焊件的形状和尺寸如图1所示,顶部接缝为圆筒形,直径100毫米,深度15毫米;环部接缝为圆环形,直径154毫米,深度20毫米。要求焊缝与母材等强度,焊后不允许焊缝和母材中存在宏观或微观裂纹,活塞     

基于Fluent的柴油机冷却环道流动特性分析

 为缓解柴油机活塞的过热问题,对冷却环道内的气液两相流动状态及传热特性进行了研究。根据计算流体力学方法确立柴油机冷却环道流动的湍流模型和相界面模型。采用有限元方法,建立冷却环道两相流仿真模型,针对柴油机不同的转速、油压和油温条件分别进行仿真计算,得出油液的体积率和平均换热系数随曲轴转角的变化规律。通过发动机喷流试验台的验证可知,冷却环道内两相流动状态的实验与仿真结果具有良好的匹配性。研究结果表明：喷油压力对油液体积率和平均换热系数的影响非常小;油体积率和平均换热系数的变化趋势不存在一致性;冷却环道的换热能力主要由油液黏度和振荡强度决定。     

活塞结构对其传热及强度的影响分析

以一款满足国Ⅴ排放限值的高压共轨柴油机活塞为研究对象,采用硬度塞测温法试验测试分析了标定功率工况下活塞稳态温度场分布和热负荷的大小,结合温度场试验测试结果建立了内冷油道与活塞的流固耦合传热数值仿真模型,仿真分析了活塞销座长度、销孔直径、火力岸高度、同侧回油孔中心间距4个活塞结构参数对活塞传热与结构强度的影响。研究结果发现,活塞的火力岸、内冷油腔、回油孔和销孔处的热流密度较大并出现应力集中。选择活塞销座长度、销孔直径、火力岸高度、同侧回油孔中心间距4个参数,进一步研究活塞结构对其传热及结构强度的影响特征。结果显示,活塞的每个结构参数值改变不仅会较大程度地改变该处的传热性能和应力分布,还会导致其他关键点的应力和温度发生改变,这使得活塞结构修改需更加谨慎。适当增加销座长度、销孔直径和火力岸高度,减小同侧回油孔中心间距,可以改善活塞的受热,也可以降低活塞的整体应力。     

Piston Assembly Design for Improved Thermal-Tribological Performance

The tribological system in the piston assembly of an internal combustion engine includes contacts at interfaces of piston/piston ring/cylinder liner, piston skirt/cylinder wall, and piston/piston pin/ connecting rod. The thermal and tribological properties of the piston, piston rings, and cylinder wall are critical to the life and quality of the engine. Severe wear and scuffing failure, especially at the ring/ring groove and ring/liner interfaces, may present a major problem if the piston temperature is too high. Temperature considerations for the piston often limit the effort to increase the engine power.

A new engine piston incorporating the heat pipe cooling technology has been developed for reducing the piston temperature, especially in the ring land and along the piston wall. The current work aims at investigating the effect of reciprocating heat pipes on heat conduction in the piston, and thus the tribological behavior of the piston assembly. Due to the high thermal conductance of the reciprocating heat pipe, a considerably large amount of combustion heat, which is conventionally conducted through the piston wall, is transferred through heat pipes. This new design will result in a lower temperature on the piston wall and a reasonably low temperature distribution in the piston.     

Investigation of heat transfer in an oil cooled piston with and without ceramic insulation on crown face

A numerical method is presented for calculating the temperature fields in a semi-adiabatic diesel engine piston having a cooling oil canal. The crown face of the piston is coated by a 2 mm thick oxide based ceramic insulating material. The non-ideal thermal contacts between the piston circumference and cylinder wall are also considered. A detailed analysis has been given for estimating the boundary conditions of the cylinder-piston assembly of an internal combustion engine. The isothermic distribution in the piston body and the heat flow rate through the different cooling media at four different engine loads have been depicted both for the cases with and without insulation coating. The results indicate a reduction (12–30%) in heat loss through the piston by use of an insulation coating at the piston crown face, assuming that both the heat transfer process from and the temperature of the combustion products remain unchanged.     

Microstructure and Mechanical Behavior of in Situ Primary Si/Mg_2Si Locally Reinforced Aluminum Matrix Composites Piston by Centrifugal Casting

Al-Si pistons are frequently damaged by burning piston top surface due to elevated combustion temperature, and by rubbing the first ring groove against the engine cylinder liner. To prevent piston from these damages, some technologies were invented, such as mounting high Ni cast iron ring around the first ring groove in Al alloy piston body and thermal resistant steel on piston top surface, and fabricating Al composite pistons by squeeze casting for enhancing the whole or local piston performance. In this paper, composite pistons locally reinforced with in situ primary Si and primary Mg2Si particles are fabricated by centrifugal casting. The microstructure characteristics, hardness and wear resistance of the composite piston are investigated and the motion characteristic of the in situ particles in centrifugal field is analyzed. The results of the experiments show that primary Si and Mg2Si particles mix up with each other in melt and segregate at the regions of piston top and piston ring grooves under the effect of centrifugal force. Particulate reinforced regions have a higher hardness and better wear resistance compared with the unreinforced regions and this performance increases after heat treatment. The analysis result of particle movement shows that, primary Si and primary Mg2Si particles move at approximately the same velocity in the centrifugal field, because of the growth of primary Si and fusion after colliding between primary Si particles, which compromised the velocity difference of primary Si and primary Mg2Si particles caused by the difference of their densities. Research results have some theory significance and applicative value of project in development of new aluminum matrix composites piston products.     

3D heat transfer,lubrication and friction coupled study for piston ring-liner on diesel engines

The piston ring and liner of internal combustion engines are generally used under increasingly harsh conditions. To investigate the mechanisms affecting the work ineffective, the coupled heat transfer, lubrication and friction model between the piston ring and liner is proposed by coupling the gas, piston set-liner, lubrication film and coolant. In this model, the temperature variation of lubricant, the gas blowby, the surface roughness, the rupture position and the non-axial symmetry of oil film are considered. The coupled heat transfer, lubrication and friction simulation is carried out for 6110 diesel engine, and the temperature fields of piston set-liner along with the corresponding lubrication and friction curves are obtained. The simulated results are verified by comparing with the temperature experiment of piston.

     

防爆柴油机活塞的热载荷响应特性研究

为提升矿用防爆柴油机的换热能力,提出水冷代替油冷方案,对燃烧室内活塞的热载荷响应特性进行了研究与分析。基于CFD方法,建立活塞冷却腔内的气液两相流模型,选用SST k-ω湍流模型,结合VOF 模型和 Level Set模型得出不同曲轴转角下的液相比例和对流换热系数变化规律,分析了冷却腔结构对传热效果的影响。构建活塞热机耦合模型,计算了极限条件下活塞的热应力和热变形。研究结果表明:冷却腔内的液相比例并非决定换热效率的唯一要素,液相的振荡作用可显著增大对流换热系数;活塞头部的薄壁变形主要受热载荷影响,受腔内压力和惯性力的影响较小。     

斯特林机活塞杆帽式组合密封动密封性能分析

为研究斯特林发动机活塞杆无油润滑帽式组合密封的动密封性能,利用有限元分析软件Abaqus建立帽式密封的二维轴对称有限元模型,基于系统实际工况,研究工质压力对帽式密封性能的影响,得到不同压力下的有效密封区域。静态密封性能分析结果表明,帽式密封环与活塞杆的接触应力是密封的关键,动态密封性能分析结果表明,两者接触应力和密封区域随压力增大而增大,且外行程接触应力略大于内行程。通过热力耦合动态仿真模拟,分析环境温度、摩擦因数、往复运动速度对动密封性能的影响。结果表明:环境温度对帽式密封温度场影响不大,热源主要来自摩擦热;往复运动速度对其密封性能影响也不大,而摩擦因数的影响较大,摩擦因数越小,帽式密封的密封效果越好,使用寿命越长。     

活塞喷油冷却流场数值模拟

近年来,随着柴油机排放及功率要求的提高,柴油机热负荷显著的增加,其中活塞热负荷问题成为柴油机进一步强化的主要限制因素之一。对于高热负荷活塞,通常采用冷却通道的办法来降低活塞温度。使用CFD工具获取表面换热系数已越来越多的用于温度场的计算,本文通过流动计算获取冷却通道壁面及活塞底面的换热系数,并分析喷油冷却流场计算结果,提出改进措施。